FIG. 8 illustrates one example of a known run-flat tire/wheel assembly. A run-flat support body 32 is attached to the inside of a pneumatic tire 31 mounted on a wheel rim 30. The run-flat support body 32 is configured by attaching elastic rings 34, 34 such as rubber to both leg end portions of an annular shell 33. The annular shell 33 is formed so that two ridge portions 33a, 33a are extended in the circumferential direction in the outer periphery.
Tubular formed bodies such as the wheel rim and the annular shell constituting the tire/wheel assembly as described above are generally made of metal because they need large strengths. As production methods thereof, casting and sheet-metal working are known. However, the former, casting, takes a long time from the injection of melted metal into a mold to the detaching of the metal from the mold, and therefore has the disadvantage that productivity is low compared to that of the latter, sheet-metal working.
Patent Document 1 discloses a method of forming a metal plate into a wheel rim. In this forming method, using a tubular blank obtained by previously processing a metal plate into a tubular shape, the tubular blank is formed by strongly pressing the peripheral wall of the tubular blank with the peripheral wall interposed between a pair of forming rollers having opposite male and female forming surfaces. However, in this forming method, large plastic deformation occurs in the side-edge portions of the peripheral wall of the wheel rim in processing. Accordingly, there is the problem that wrinkles and ruptures are prone to appear because excessively large strain concentrates in the vicinities thereof. In particular, when a metal material having a larger breaking stress is used in order to improve the strength, wrinkles and ruptures are significantly more prone to appear.
On the other hand, Patent Document 2 discloses a method of forming an annular shell of a run-flat support body. In this forming method, while a tubular blank made of a metal plate is being rotated, the peripheral wall thereof is interposed between forming rollers from inside and outside to be pressed, whereby a ridge portion continuing in the circumferential direction is formed. However, as in the case of the above-described wheel rim forming method, there is the problem that when both side-edge portions of the tubular blank are bent, wrinkles and ruptures are prone to appear in the vicinities thereof. In particular, when a metal material having a larger breaking stress is used in order to improve the strength, wrinkles and ruptures are significantly more prone to appear.
Patent Document 1: Japanese Patent application Kokai publication No. Sho 57-175401
Patent Document 2: German Patent DE10149086C1